%I #5 Mar 31 2012 10:32:39
%S 2,3,19,157,2917
%N Number of digits in Mersenne primes with a prime number of digits.
%e a(4) is M21, the 21st Mersenne prime with prime digit count of 2917
%Y Cf. A028335.
%K nonn,base
%O 1,1
%A _Enoch Haga_, Dec 18 2001